A switching power converter of the present invention, wherein a series circuit comprising the primary winding 31 of a transformer and a first switch 2 is connected in parallel with a DC input power supply 1, and a series circuit comprising a capacitor 8 and a second switch 7 is connected in parallel with the primary winding 31; the switching power converter is provided with a first control drive circuit 9 for alternately turning on/off the first switch 2 and the second switch 7 so as to have an on-period, an off-period and a rest period, and a second control drive circuit for turning on/off the third switch 41 connected to the secondary winding 32 of the transformer, whereby the current flowing through the secondary winding of the transformer has a resonance waveform.